//方法一
void my_strcat(char des[], char src[])
{
    int i = 0, j = 0;
    while(des[i]) i ++;
    while(src[j])
    {
        des[i ++] = src[j ++];
    }
    des[i] = '\0';
}
//方法二
char *my_strcat(char *pdes, char *psrc)
{
    char *pt = pdes;
    while(*pdes) pdes ++;
    while(*psrc)
    {
        *(pdes ++) = *(psrc ++);
    }
    *pdes = '\0';
    return pt;
}
//方法三
char *my_strcat(char *des, const char *src)
{
    char *ret = des;
    //assert(des != NULL);
    //assert(src != NULL);
    while(*des ++ = *src ++)
    {
        ;
    }
    return ret;
}